|
|
Atomic Number: |
53 |
Melting Point: | 113.7 ºC | |
| Atomic Symbol: | I | Boiling Point: | 184.4 ºC | ||
| Atomic Weight: | 126.9045 amu | Density: | 4940
kg/m 3 |
||
| Atomic Radius: |
133.3 pm |
Oxidation States: | 5, 7, -1 | ||
| Covalent Radius: | 133 pm | Electron Configuration: | [Kr]5s24d105p5 | ||
| van der Waals Radius: |
198 pm |
State of Matter: | solid (nonmagnetic) |
(Gr. iodes: violet) Discovered in 1811 by Courtois. He was the son of a manufacturer of saltpeter (potassium nitrate), a vital part of gunpowder. At the time France was at war and gunpowder was in great demand. Saltpeter was isolated from seaweed washed up on the coasts of Normandy and Brittany. To isolate the potassium nitrate, seaweed was burned and the ash then washed with water. The remaining waste was destroyed by adding hydrochloric acid. One day Curtois added too much sulfuric acid and cloud of purple vapor rose. Curtois noted that the vapor crystallized on cold surfaces making dark crystals. Curtois suspected that this was a new element but lacked the money to pursue his observations.
Iodine is a bluish-black, lustrous solid, volatizing at ordinary temperatures into a blue-violet gas with an irritating odor; it forms compounds with many elements, but is less active than the other halogens, which displace it from iodides. Iodine exhibits some metallic-like properties. It dissolves readily in chloroform, carbon tetrachloride, or carbon disulfide to form beautiful purple solutions. It is only slightly soluble in water.
Iodine occurs sparingly in the form of iodides in sea water from which it is assimilated by seaweeds, Chilean saltpeter, nitrate-bearing earth (known as caliche), brines from old sea deposits, and in brackish waters from oil and salt wells.
Ultra pure iodine can be obtained from the reaction of potassium iodide with copper sulfate. Several other methods of isolating the element are known.
Iodine compounds are important in organic chemistry and very useful in medicine. Iodides, and thyroxine which contains iodine, are used internally in medicine. Tincture of iodine (3% elemental iodine in water/ethanol base) is an essential component of any emergency survival kit, used both to disinfect wounds and to sanitize surface water for drinking (3 drops/L, let stand for 30 minutes). Potassium iodide (KI) finds use in photography and tablets can be given to people in a nuclear disaster area because it prevents the body from absorbing the radioactive iodine produced at the disaster area. The deep blue color with starch solution is characteristic of the free element. Tungsten iodide is used to stabilize the filaments in light bulbs. Nitrogen triiodide is an explosive, too unstable to be used commercially.
An iodine deficiency is called endemic goitre. This is usually prevented by the addition of small amounts of sodium iodide to table salt, the result is known as iodized salt.
Thirty isotopes are recognized. Only one stable isotope, 127I is found in nature. The artificial radioisotope 131I, with a half-life of 8 days, has been used in treating the thyroid gland as well as a tracer in medicine. The most common compounds are the iodides of sodium and potassium (KI) and the iodates (KIO3).
Care should be taken in handling and using iodine, as contact with the skin can cause lesions; iodine vapor is intensely irritating to the eyes and mucus membranes. The maximum allowable concentration of iodine in air should not exceed 1 mg/m3 (8-hour time-weighted average - 40-hour).
